[OSGeo-Discuss] 'lossless' JPEG2000

[Ed McNierney]

Christopher -

You will very likely find that using different LZW compression options (particularly setting a small strip size) will slightly degrade compression performance while significantly improving read time.  While I think your test data are valid, they only address one of many possible configurations and I wouldn't necessarily make broad generalizations about LZW from them.

However, I have generally found that LZW compression for photographic data is indeed not a good choice; I'm surprised you got it to perform as well as you did (in compression).

	- Ed

Ed McNierney
Chief Mapmaker
Demand Media / TopoZone.com
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: 978-251-4242, Fax: 978-251-1396
ed at topozone.com

-----Original Message-----
From: discuss-bounces at lists.osgeo.org [mailto:discuss-bounces at lists.osgeo.org] On Behalf Of Christopher Schmidt
Sent: Monday, February 25, 2008 8:57 PM
To: discuss at lists.osgeo.org
Subject: Re: [OSGeo-Discuss] 'lossless' JPEG2000

On Mon, Feb 25, 2008 at 04:31:34PM -0800, Michael P. Gerlek wrote:
> Yup: Kakadu is not Open Source, as per the OSI definition of the term.
> The only FOSS package I know of is OpenJpeg2000 (or something like
> that); unfortunately, however, it is not suitable for geo-sized imagery
> last time I looked.

Yep.

> (LZW tiffs are a reasonable option, as they are lossless and the LZW
> patent issues have faded into the sunset.)

The level of compression from LZW is poor by comparison, on aerial
imagery: a test dataset compressed from 169MB to 83MB, and time to serve
up a small portion was approximately the same as with JPG (6.1s jpg,
6.5s lzw, .5s uncompressed), but the JPG was compressed to 13MB, making
it worth the cost; lzw doesn't pay for itself in the same way.

(See numbers on http://wiki.openaerialmap.org/Serving_Data)

Regards,
-- 
Christopher Schmidt
Web Developer
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